Josh Quillin created this video about Lenses so people don't need to ask the basic questions. 

You might not be a cinematographer, or even in a camera crew, but that doesn't mean it isn't helpful to know exactly how lenses work! Any filmmaker in any department of the crew can benefit from knowing the basics. Shockingly these aren't even things you'll learn in every film school. 

But that's what we're here for. 

Source: Josh Quillen